1. Field of the Invention
The present invention relates to a plasma display panel (PDP) which is a kind of light-emitting device for displaying an image by using the gas discharge between glass substrates and, more particularly, to a color PDP having an internal structure improved to increase aperture rate of the front panel which is an image displaying surface and maximize the efficiency of light emission using discharge between electrodes.
2. Background of the Related Art
In general, color PDPs are a kind of light-emitting device for displaying an image by use of internal gas discharge. Color PDP's are advantagous in that: (1) PCP's do not require active elements in cells; (2) each cell of the PDP has a simple fabricating process; and (3) PDP's have a high response speed.
In addition, PDPs are more easily enhanced in size relative to existing liquid crystal displays and can be used for large-sized display devices over 40 inches.
The schematic structure of PDPs includes two glass substrates bonded together with a frit glass and sealed to form an integrated body. The sealed internal space between the two glass substrates is filled with a gas under a pressure of 100.about.600 Torr where the gas may be Xenon (Xe) in Helium (He).
The image display section of a panel has intersections between a plurality of electrodes in correspondence to pixels (cells). When driving the panel to display an image, a voltage greater than 100 volts is applied to the intersections causing glow discharge of gas and emitting lights. This panel section is combined with a driving section to serve as a display device.
PDPs are classified into two-, three- and four-electrode types according to the number of electrodes allotted to each cell: the two-electrode type PDP is driven by applying an addressing and sustaining voltage to two electrodes. The three-electrode type PDP is generally called a "surface discharge type" and is switched or maintained by a voltage applied to an electrode positioned on the lateral side of a discharge cell.
An example of the related art three-electrode surface discharge PDP will be described below in reference with FIGS. 1 to 3.
FIG. 1 is an exploded view of a related art PDP structure having upper and lower substrates. In the figure, a front substrate 1 which is an image displaying surface is combined in parallel with a back substrate 2 at a predetermined distance.
The front substrate 1 is provided with a sustain discharge electrode formed with a pairing of a common electrode C and a scan electrode S. The sustain discharge electrodes are used to sustain light-emission within cells by means of mutual discharges in a pixel.
The front substrate 1 may also be provided with a dielectric layer 5 for restraining a discharge current of the two electrodes and insulating between electrode pairs. Additionally, a protective layer 6 may be formed on the dielectric layer 5.
The back substrate 2 includes a plurality of spaces for discharge with separate walls 3 forming cells, a plurality of address electrodes A formed in the direction parallel with the separate walls 3 for performing address discharge at the intersections with scan electrodes S which creates vacuum ultra-violet rays, and a fluorescent layer 4 formed on the lateral sides of separate walls 3 and on the back substrates out of the internal surface of each discharge space for emitting visible rays to display images during address discharge.
FIG. 2 illustrates the arrangement of common electrodes C, scan electrodes S and address electrodes A.
FIG. 3 is a cross-sectional view of a cell after the upper and lower substrates are bonded together to form an integrated body, in which the lower substrate is rotated at 90 degrees for better understanding.
First, when a discharging voltage is applied between a scan electrode S and a common electrode C that form a pair of electrodes in the cell, surface discharge occurs between the two electrodes to form wall charges on the internal surface of the discharge space.
Following the surface discharge, an address discharge voltage is applied to the scan electrode S, and the address electrode A causes writing discharge to occur in the cell. Subsequently, a sustain discharge voltage is applied to the scan electrode S and the common electrode C. A sustained discharge occurs due to charged particles being generated in the address discharge between address electrode A and scan electrode S. Thus sustaining light-emission of the cell for a predetermined period of time.
In other words, an electric field is formed in a cell due to discharge between electrodes such that a minute quantity of electrons contained in a discharge gas are accelerated and collide with neutral particles in the gas to ionize. Thus, generated electrons collide with another neutral particles to produce more electrons and ions. In turn, the discharge gas is changed into plasma and vacuum ultra-violet rays are generated. The generated ultra-violet rays excite the fluorescent layer 4 to emit visible rays, which are projected to the outside through the front substrate 1 to cause light-emission in a cell.
In the prior art PDP structure as described above, sustain discharge electrodes C and S are fabricated in such a manner that transparent electrodes are patterned in order to prevent reduction of the aperture rate of front substrate 1 on which an image is formed. A metal having a lower resistance than the transparent electrodes is applied to the lateral edge of the transparent electrodes to prevent deterioration of the display quality.
Despite the use of transparent electrodes, there is a loss of about 10 to 25% of visible rays because the sustain discharge electrodes C and S are positioned in the front substrate 1.
The contrast characteristic becomes deteriorated because the light-emitting part is completely exposed to the outside and the reflection factor is high. To enhance the contrast characteristic, use is made of a color filter in spite of deterioration of luminance by about 30 to 50%.
As a measure to enhance the luminance, raising the driving voltage applied to electrodes may increase the amount of generated vacuum ultra-violet rays, which raises production costs in realizing peripheral circuits and causes a rapid reduction of life of the PDP.